Oxide Semiconductor Transistor Buffer Layer for High Voltage Reliability
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Solution Overview
Problem
Transistors used in display devices often have negative threshold voltages, leading to normally-on states, making it difficult to control current flow and affecting the performance of active-matrix display devices, especially when high voltage or large current is involved.
Innovation Solution
A semiconductor device structure is developed with an oxide semiconductor layer, a nitrogen-containing buffer layer, and a nitrogen-containing metal oxide gate electrode layer, which helps in achieving a positive threshold voltage, enabling normally-off switching and improving reliability under high voltage or large current conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional transistor structures are used, then manufacturing is simpler, but the threshold voltage becomes negative causing normally-on state
Solution Approach 1:
The gate electrode layer is divided into multiple layers with different materials and functions. The first gate electrode layer (G1) is formed of a metal oxide containing nitrogen to control threshold voltage, while the second gate electrode layer (G2) is formed of a different metal oxide to provide additional control. This segmentation allows independent optimization of threshold voltage control and switching performance.
Solution Approach 2:
The transistor employs composite material structures: the gate electrode layer uses a stacked configuration of different metal oxides (G1 and G2), the source and drain electrodes use composite structures (S1/S2 and D1/D2), and buffer layers are positioned between the semiconductor layer and electrodes. These composite structures enable simultaneous achievement of positive threshold voltage and low contact resistance.
2Ease of operation
If the threshold voltage is negative, then the transistor is in normally-on state, but it becomes difficult to control current flow
Solution Approach 1:
The threshold voltage is controlled by changing the material composition and structure of the gate electrode layer. By using a metal oxide containing nitrogen in the first gate electrode layer and adjusting its thickness and composition ratios, the threshold voltage is shifted to positive values, enabling normally-off operation and improving circuit control reliability.
3Power
If high voltage or large current is involved, then display performance improves, but transistor reliability decreases
Solution Approach 1:
Buffer layers are positioned between the semiconductor layer and the source/drain electrodes to prevent direct contact and reduce stress concentration. These buffer layers act as protective interfaces that cushion the semiconductor layer from high voltage and large current stress, preventing degradation and improving transistor durability under high-power operating conditions.
Data Source
AI summary
A semiconductor device having a novel structure or a method for manufacturing the semiconductor device is provided. For example, the reliability of a transistor which is driven at high voltage or large current is improved. For improvement of the reliability of the transistor, a buffer layer is provided between a drain electrode layer (or a source electrode layer) and an oxide semiconductor layer such that the end portion of the buffer layer is beyond the side surface of the drain electrode layer (or the source electrode layer) when seen in a cross section, whereby the buffer layer can relieve the concentration of electric field. The buffer layer is a single layer or a stacked layer including a plurality of layers, and includes, for example, an In—Ga—Zn—O film containing nitrogen, an In—Sn—O film containing nitrogen, an In—Sn—O film containing SiOx, or the like.